Some data on the biology of Polymetme corythaeola (Phosichthyidae), from off the Portuguese south coast, North East Atlantic

3 Pages·2001·0.14 MB·English

by  Marques, A M

SOME DATA ON THE BIOLOGY OF 2.2 m high and 23 m wide) with a 35 mm shrimp
POLYMETME CORYTHAEOLA (PHOSICH- net was used. Towing speed was around 2 knots.
THYIDAE), FROM OFF THE PORTUGUESE Three sampling operations provided 47 Po-
SOUTH COAST, NORTH EAST ATLANTIC. lymetme corythaeola: 10 from 650 m, 31 from 620
Afonso MARQUES, Laboratório Marítimo da m and 6 from 330 m deep. All specimens were
Guia, IMAR, Universidade de Lisboa, Faculdade frozen aboard the ship. At the laboratory, 22 males
de Ciências Estrada do Guincho, 2750 Cascais, and 25 females were measured and weighted, their
PORTUGAL. [[email protected]] stomach extracted and the contents analysed under
a stereomicroscope. Female gonads were analysed
RÉSUMÉ.!-!Quelques données sur la biologie de macroscopically using the following maturity
Polymetme corythaeola (Phosichthyidae) sur la scale: Stage I - no visible oocytes; Stage II -
côte sud du Portugal, Atlantique nord est. visible oocytes; Stage III - large oocytes; Stage IV
Le régime alimentaire et les rapports en- - translucent large oocytes and Stage V - flaccid
tre la bathymétrie, l’indice gonado-somatique et le gonad with few oocytes in Stage IV. They were
sexe-ratio d’une espèce benthopélagique, Poly- weighted fresh and the gonado-somatic index was
metme corythaeola capturée sur la côte sud du calculated (GSI = gonad weight!/!body weight x
Portugal, sont décrits. Le sexe-ratio semble dé- 100).
pendre de la bathymétrie. Les euphausiacés ont été The number of individuals with stomach
les seules proies observées. contents under the total number of individuals
expressed the vacuity index. Specimens were
Key!words. - Polymetme corythaeola - ANE - studied separately by depth and those lacking any
Portugal - Diet - Sex-ratio - Gonado-somatic field data were discarded.
index. The species is distributed between 330
and 650 m deep in the survey (Table I) and only
adults were caught. The largest specimens, both
Polymetme corythaeola (Alcock, 1898), males and females, were captured at 330 m deep.
is a dioecious benthopelagic fish that inhabits off Only the gonado-somatic values of females was
continental and island slopes and seamounts of all calculated for every depth. The results show that,
3 major oceans, mainly at depths of 300-500 m. It at least in January, spawning females arise from
is the only species of this genus known in the deep to shallow waters (Fig.!2).
CLOFNAM area (Badcock, 1984). Its distribution The females provided by the 330 m haul
ranges from northwest Africa and to the coasts of showed gonads at stage IV and V, indicative of a
Lisbon, with the northern record at 51°39.7’N- spawning period. Stomach content analyses
14°16.5’W. It is absent in the Mediterranean showed that crustaceans were the main prey and
(Badcock, 1984). It is a by-catch species on the one Meganyctiphanes norvegica, an eucarid
Portuguese slope below 300 m (Saldanha, 1966). crustacean of the family Euphausiidae was identi-
The Deep Resources Cruises team from fied. No stomach eversion was observed and the
the Portuguese Institute of Marine Research estimated vacuity index was 0.50.
(IPIMAR), surveyed the Portuguese south coast in At 620 m deep the individuals were
January 1995 (Fig. 1), aboard the NI “Noruega”. smaller than at 330 m and the females were larger
A commercial otter trawl (mouth opening than males. Sex-ratio was about 1:1 (16 females
Table!I.!-!Mean total length, mean weight, mean gonad weight and mean gonado-somatic index of
Polymetme corythaeola specimens at each depth.
Cybium 2001, 25(1): 100-102.
Biology of Polymetme corythaeola from Portuguese coast 101
Fig.!1.!-!Sampling area (1) where specimens of Polymetme corythaeola were caught (300-650 m deep).
Fig.!2.!-!Gonad weight (GW) and gonado-somatic index (GSI) of Polymetme corythaeola females (total
number = 25) collected during the cruise (values are presented in ascending order).
and 15 males): 1 female in stage I; 8 in stage II; 1 M.!norvegica were identified in 10 stomachs with
in stage III; 3 in stage IV and 1 in stage V. Com- food. Vacuity index was 0.68 and the mean num-
pared with those from the previous sample, the ber of prey per stomach rounds 2.6.
macroscopic observation and gonado-somatic Fishes from the 650 m haul had the same
proportions suggest that at this depth fishes are size range as those of the 330 m haul. This sample
going through a pre-spawning gonad growing was comprising 10 specimens - all females - 4 of
period. No stomach eversion was observed and 26 them in stage II and 5 in stage III (one specimen
102 MARQUES
lacking data was discarded). Gonado-somatic REFERENCES
index varied from 0.392 to 5.016. Also a gonad
growing period was detected in these samples. All BADCOCK J., 1984.!-!Photichthyidae. In: Fishes
these specimens had their stomachs full, the only of the North-eastern Atlantic and the
observed prey being 18 M.!norvegica. Mediterranean (Whitehead P.J.P., Bauchot
Polymetme corythaeola has, at least, a M.-L., Hureau J.-C, Nielsen J. & E.
spawning period in January and females seems to Tortonese, eds), pp.!318-324. Paris:
seek shallower waters to spawn. Since this species UNESCO.
does not evert the stomach during hauling we SALDANHA L., 1966.!-!Polymetme corythaeola,
conclude that crustaceans exclusively constitute its espèce nouvelle pour la faune du Portugal
diet, namely the benthopelagic euphausid (Pisces, Gonostomatidae). Arq. Museu Bo-
M.!norvegica. cage, (2ª série) Vol.I, Notas e Suplementos, 7:
27-32.
Acknowledgements. - Thanks are due to the late SCHAEFER S., JOHNSON R.K. & J.
Prof. Luiz Saldanha, coordinator of EU-MAST 2 BADCOCK, 1986.!-!Photichthyidae. In:
Project, for the scientific support. We are also Smith’s Sea Fishes (Smith M.M. & P.C.
grateful to the former President of IPIMAR, Heemstra, eds), pp.!243-247. Berlin: Sprin-
Carlos Sousa Reis who made the oceanographic ger-Verlag.
vessel NI “Noruega” available for sampling
operations. Our colleague Ana Colaço made the
work aboard ship much easier. This work was
partially funded by the EC MAS 2 CT 920033 Reçu le 27.01.2000.
Contract. Accepté pour publication le 04.12.2000.